The delivery of volatile materials, such as fragrances, e.g., air fresheners, may be achieved by means of a delivery apparatus that includes a reservoir containing volatile material. The delivery apparatus or delivery device typically includes a vapor permeable membrane that covers or encloses the reservoir. Volatile material within the reservoir passes through the vapor permeable membrane and is released into the atmosphere, e.g., air, on the atmospheric side of the membrane. Vapor permeable membranes are typically fabricated from organic polymers and are porous.
The rate at which volatile material passes through the vapor permeable membrane is generally an important factor. For example, if the rate at which volatile material passes through the vapor permeable membrane is too low, properties associated with the volatile material, such as fragrance, will typically be undesirably low or imperceptible. If, on the other hand, the rate at which volatile material passes through the vapor permeable membrane is too high, the reservoir of volatile material may be depleted too quickly, and properties associated with the volatile material, such as fragrance, may be undesirably high or in some instances overpowering.
It is also generally desirable to minimize or prevent the formation of liquid volatile material on the atmospheric or exterior side of the vapor permeable membrane, from which the volatile material is released into the atmosphere, e.g., into the air. Liquid volatile material that passes through the exterior side of the vapor permeable membrane may collect, e.g., puddle, within or on the exterior side of the membrane and leak from the delivery device resulting in, for example, staining of articles, such as clothing or furniture, that come into contact with the liquid volatile material. In addition, the formation of liquid volatile material on the exterior side of the vapor permeable membrane may result in the uneven release of volatile material from the delivery device.
Further increases in ambient temperature may increase the rate at which volatile material passes through the vapor permeable membrane to undesirably high rates. For example, a delivery device that is used within the passenger compartment of an automobile may be exposed to increases in ambient temperature. As such, minimizing the increase in the rate at which volatile material contained within the device passes through the vapor permeable membrane, as a function of increasing ambient temperature, is typically desirable.
It would be desirable to develop new microporous materials that possess controlled volatile material transfer properties. It would be further desirable that when such newly developed microporous materials are used as a vapor permeable membrane in a delivery device, the microporous material minimizes the formation of liquid volatile material on the exterior side or surface of the membrane. In addition, the rate at which volatile material passes through such microporous materials should increase minimally with increases in ambient temperature.